Methods and apparatus for counter-current leaching of finely divided solids

ABSTRACT

This disclosure describes systems, methods, and apparatus for counter-current solids leaching. A multi-stage countercurrent leaching chamber can include a top and bottom end, a barren liquor input, two or more regions for countercurrent mixing, and a barren solids output. The input can be configured to receive barren liquor. The two or more regions for countercurrent mixing and separation can be configured to mix and separate liquid and solid phases. The barren solids output can be configured to collect and discharge barren solids from the bottom end of the multi-stage countercurrent leaching chamber. A fluidized bed chamber and clarifier chamber can also be included, where the fluidized bed receives a fluidizable slurry of pregnant solids and the clarifier chamber aids in separating liquids from solids passing from a top of the fluidized bed chamber to the top end of the multi-stage countercurrent leaching chamber.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 120

The present Application for Patent is a continuation of patentapplication Ser. No. 15/010,890 entitled “METHODS AND APPARATUS FORCOUNTER-CURRENT LEACHING OF FINELY DIVIDED SOLIDS” filed Jan. 29, 2016which claims priority to Provisional Application No. 62/114,444 entitled“METHODS AND APPARATUS FOR COUNTER-CURRENT LEACHING OF FINELY DIVIDEDSOLIDS” filed Feb. 10, 2015, and assigned to the assignee hereof andhereby expressly incorporated by reference herein.

FIELD OF THE INVENTION

The present disclosure relates generally to solid waste treatment. Inparticular, but not by way of limitation, the present disclosure relatesto systems, methods and apparatuses for separation and removal ofsoluble species from insoluble, finely divided dry solids, or finelydivided solids present in the form of paste, sludge, or slurry.

BACKGROUND OF THE INVENTION

Drilling for oil and gas produces large quantities of drill cuttings anddrilling fluids that are comprised of mixtures of finely divided solids(silt, clay, pulverized formation minerals, barite, etc.) that are oftensaturated with, or suspended in, salt brine and/or organic liquid. Thesedrilling residues require expensive disposal to protect human health andthe environment.

When deposited on the landscape or simply buried, drilling residues poseunacceptable environmental hazards due to leaching of salt and organicspecies by water from natural precipitation that leads to ground- andsurface water contamination. Attempts to stabilize drilling residue byaddition of fly-ash, cement kiln dust, or other solidifying agentsbefore burial, also have proven ineffectual and unsatisfactory largelybecause the salts and organic species remain leachable. Consequently,the current primary means of disposal of drilling residues issolidification, transport, and disposal in a hazardous waste landfill.

Solidification of oily drilling residues is most often accomplished bycentrifugation or thermal desorption to remove the organic phase.Residual solids from centrifugation contain both leachable organic andinorganic (salt) species. Residual solids from thermal desorption alsocontain leachable salts. These solidified residues cannot beland-disposed on-site and must, instead, be transported and disposed ata hazardous waste landfill incurring substantial additional costs.

Solidification of drilling residues comprised of brine muds and cuttingsis most often accomplished by addition of drying agents such as fly-ashor cement kiln dust. These means of solidification of drilling residueincrease both the mass and volume of material that must be transportedand disposed in a landfill, which increases both transportation anddisposal costs.

In order to avoid the expense and liabilities associated withtransportation and landfilling of hazardous drilling residues, it isdesirable to render said residues suitable for land-spreading or othermeans of on-site disposal. On-site disposal of drilling residuesrequires means to separate soluble or leachable salts from finelydivided dry solids or finely divided solids present in the form ofpaste, sludge, or slurry.

Those skilled in the art will recognize that the greatest impediment toefficient leaching or washing of fine solids is caused by the amount ofinterstitial liquor present in saturated fine sediments and thedifficulty of separating said interstitial liquor from the surroundingfine solids.

Settled, saturated fine solids derived from drilling with salt brinemuds exhibit void fractions in the range from about 40% to 55% yieldingmass fractions of interstitial liquid in the range from about 20% to 35%depending on solids particulate density and concentration of salt in theinterstitial liquor. If the salt concentration in the interstitialliquor is near saturation, say 24% by mass, then batch-wise washing ordilution with fresh water implies consumption of very large quantitiesof salt-free water in order to render saturated solids containingacceptably low concentrations (<1,000 mg/kg) of salt as required foron-site disposal.

For example, if an aliquot of saturated cuttings exhibiting a settledvoid volume of 40% is washed with a void volume of salt free water, thesettled residue after washing will exhibit interstitial fluid havingone-half the initial concentration of salt. Each successive washingstage will reduce the concentration of salt in the interstitial fluid byhalf again. Therefore, it would require 7 stages of washing, settlingand decanting to reduce the concentration of salt from saturation(240,000 mg/L) to below 2,000 mg/L in the final interstitial fluid.Total wash water consumption would be 2.8 volumes per volume ofsaturated solids treated.

For on-site treatment, where fresh water needs to be transported to thesite, using minimum wash water is an economic and logistical imperative.Analysis shows that the total amount of wash water needed to achieve aspecified degree of salt removal is inversely proportional to the numberof washing stages used. Furthermore, the minimum mass ratio of washwater to solids treated for a specified degree of salt removal isachieved by using a true counter-current, multistage, contacting regime.An additional advantage of using minimum wash water is that lowervolumes of higher-concentration pregnant liquor are produced. Since highconcentration dense brine has value in the oil field, thecounter-current cuttings leaching system has the potential to greatlyreduce disposal costs, or produce a merchantable product from drillingresidues.

Disclosed herein are methods and apparatus for accomplishing truecounter-current, multistage, washing and leaching, to remove solublesalts from finely divided dry solids, or finely divided solids presentin the form of paste, sludge, or slurry, while producing a low volume ofhigh concentration pregnant liquor for re-use or sale.

Those skilled in the art will recognize that disclosed methods andapparatus may be applied to other industrial separations, including butnot limited to, decontamination of soils, mineral and ore beneficiation,recovery of fertilizer values from cement kiln dust, recovery ofchemical values from waste solids, regeneration of ion exchange resinsand adsorption media, and performing numerous liquid/solid andliquid/liquid extractions.

SUMMARY OF THE DISCLOSURE

Exemplary embodiments of the present invention that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

Some embodiments of the disclosure may be characterized as an apparatusfor leaching fine solids. The apparatus can include a multi-stagecountercurrent leaching chamber having: a top end; a bottom end; abarren liquor input configured to receive barren liquor; two or moreregions for countercurrent mixing and separation of liquid and solidphases; and a barren solids output configured to collect and dischargebarren solids from the bottom end of the multi-stage countercurrentleaching chamber. The apparatus can also include a fluidized bed chamberwith a top and bottom end, and joined at its top end with the top end ofthe multi-stage countercurrent leaching chamber, the fluidized bedchamber including a pregnant solids input configured to receive afluidizable slurry of pregnant solids. The apparatus can further includea clarifier chamber with a top and a bottom end, and joined at itsbottom to the top end of the multi-stage countercurrent leaching chamberand the top end of the fluidized bed chamber.

Other embodiments of the disclosure may be characterized as a method forleaching fine solids. The method can include receiving barren liquor andpregnant solids near a bottom of a fluidized bed to form a mixture. Themethod can also include fluidizing the mixture to form a fluidizedmixture that moves toward a top of the fluidized bed. The method can yetfurther include the fluidized mixture entering a region near a top ofthe fluidized bed that is shared with a top of a multi-stagecountercurrent leaching chamber, the region having a larger crosssection than a cross section of either the fluidized bed or themulti-stage countercurrent leaching chamber alone. Yet further, themethod can include receiving a leach or wash solution near a bottom ofthe multi-stage countercurrent leaching chamber. Additionally, themethod can include allowing the pregnant solids to descend within themulti-stage countercurrent leaching chamber via the force of gravity.Yet further, the method can include separating solids and liquids viamultiple mixing and separating stages of the multi-stage countercurrentleaching chamber. Moreover, the method can include collecting anddischarging barren solids from a bottom of the multi-stagecountercurrent leaching chamber. Finally, the method can includecollecting and discharging pregnant liquor from a clarifier arrangedatop both the fluidized bed and the multi-stage countercurrent leachingchamber.

BRIEF DESCRIPTION OF FIGURES

Various objects and advantages and a more complete understanding of thepresent disclosure are apparent and more readily appreciated byreferring to the following detailed description when taken inconjunction with the accompanying drawings:

FIG. 1 illustrates one embodiment of a counter-current solids leachingsystem.

FIG. 2 shows an integrated process flow diagram using thecounter-current solids leaching system for treating drill cuttings.

FIG. 3 shows one embodiment of a method for counter-current solidsleaching.

DETAILED DESCRIPTION

FIG. 1 shows one embodiment of a counter-current flow, solids leachingsystem 100 comprised of a multistage leaching chamber 101 fitted withinter-stage thickener plates 102, and separated from a fluidized bed 103by a vertical overflow weir 106. The leaching chamber 101 and fluidizedbed 103 are connected at their upper end to a sedimentation clarifier105.

Pregnant solids are fed to the lower portion of the fluidized bed 103where they are fluidized by recycled fluidizing liquor that isintroduced to the bottom of the fluidized bed chamber via a fluidizingliquor distributor 104. Those skilled in the art will recognize that thefluidizing liquor distributor 104, without limitation, may be selectedfrom the group consisting of screens, perforated plates, perforatedtubes, sintered metal or plastic plates, tuyer plates, bubble capplates, dense media, and open tubes.

Fluidized solids rise vertically in the fluidized bed 103 and aretransported to the region of the top of the overflow weir 106 where thesuperficial velocity of the fluidizing liquor is reduced below theminimum fluidizing velocity for the solids. The reduction in fluidizingvelocity occurs as the fluidized bed expands into the increased crosssection provided by the combined leaching chamber 101 and fluidized bed103.

The clarifier 105 further increases the cross section and reduces theupward component of velocity of the up-welling fluidizing liquor suchthat all but the finest particles settle by gravity into the leachingchamber 101.

Solids slide down the inclined thickener plates 102 to the plate gapsand fall over the plate precipice in a thin sheet. The downward velocityof the falling sheet is much greater than the Stokes settling velocityof any individual particle in the sheet. The falling sheet of solids isintercepted by counter flowing leach or wash solution, having asubstantial horizontal streamline component. The wash water partiallyfragments the falling sheet of solids and pushes it toward the outsidewall of the leaching chamber 101. Near the wall, the wash solutionstreamline is forced back to upward vertical, creating a shear zone, inthe thickener plate gap, between the falling and fragmenting sheet ofsolids and the rising wash water stream. Some of the falling solids arere-entrained by the upward flow of wash water and are carried into theinterstitial volume above the plate.

The interstitial volume above each thickener plate 102 receives solidsfalling from the plate above and solids re-entrained by the wash watermoving through the plate gap from below. In the interstitial volumeabove the plate, wash water moves in a substantially horizontalstreamline across the column, to the opposing gap, and above the bulk ofthe disbursed solids. This promotes settling and transport of solidsdown the plate. Sweep flock settling is the predominant mechanism inthis region, with larger flocks and particles, carrying finer materialsdownward to the thickener plate and occluding them in the sheetdischarge. In this manner, the concentration of solids in the regionabove the plate increases until the settling, transport, and sheetdischarge reach steady state equilibrium with the sludge solids feedrate. Each stage provides a turbulent contact zone and a quiescentsettling zone. Downward transport of particles is not governed by Stokeslaw, and the solids loading to the pregnant liquor discharge isdetermined by the dimensions of the sedimentation clarifier 105.

FIG. 2 shows one embodiment of an integrated process flow diagram 200for employing the counter-current flow solids leaching system 100 toremove dissolved solids from finely divided drilling residues, alsoreferred to as cuttings.

Cuttings feed in the form of dry solids or solids present as paste,sludge, or slurry are fed to a feed pump 201 where they are comingledand mixed with filter cake from a blowback filter 202 before being fedto the previously disclosed counter-current flow solids leaching system100.

Those skilled in the art will recognize that the feed pump 201, withoutlimitation, may be selected from the group consisting of high-shearmixers, pug mills, mixing tanks, progressive cavity pumps, rotary lobepumps, flexible impeller pumps, rotary valves, and centrifugal slurrypumps.

Pregnant liquor discharged from the counter-current flow solids leachingsystem 100 is filtered using a blow-back filter 202 to produce clarifiedproduct brine for beneficial use or disposal, plus a thickened filtercake that is recycled to the feed pump 201.

Those skilled in the art will recognize that the blow-back filter 202,without limitation, may be selected from the group consisting of bagfilters, belt filters, filter presses, V-Sep filters, sintered metalfilters, ceramic filters, deep bed filters, lamella thickeners,sedimentation clarifiers, electro-coagulation clarifiers, andcentrifugal clarifiers.

Recycle of pregnant liquor to the feed pump and fluidized bedconcentrates soluble salts in the recycled fluid and maximizes theconcentration and specific gravity of the product brine. High specificgravity brines have value in the oil field. In addition,high-concentration brines exhibit reduced volume and reduced cost fortransportation and off-site disposal via deep well injection.

Settled, barren solids exiting the bottom of the counter-current flowsolids leaching system 100 may be dewatered using a dewatering screwpress 203 or other dewatering equipment. Dewatering produces a reducedvolume, reduced mass, stackable, easily handled and transported solidresidue. Water thus removed from the barren solids may be comingled withthe leach or wash solution fed to the leaching system 100 in order toreduce the total fresh solution required for operation of the system.

Those skilled in the art will recognize that the dewatering press 203,without limitation, may be selected from the group consisting ofdewatering screw presses, belt filters, pressure filters, V-Sep filters,gas displacement dryers, and centrifugal separators.

Operational Experience

A prototype commercial countercurrent solids leaching system as shown inFIG. 2 has been operated on a drilling site in the Williston basin totreat salt water brine mud cuttings and other solid residues derivedfrom horizontal drilling operations in the Bakken formation. Theprototype commercial countercurrent solids leaching system demonstratedremoval of 98.8% to 99.4% of chlorides from feed materials containing anaverage of 57,315 mg Cl⁻/L, and at feed rates as much as 20% above thesystem design rating. Treated material exhibited chloride concentrationsbelow the regulatory limit for surface application of 250 mg/kg.

The instant invention has been reduced to practice and successfullydemonstrated at the prototype commercial scale throughput of 500 lbm/hr,and with feed material-to-fresh water mass ratios in the range from 1.2to 4.6. Demonstration testing showed that the prototype countercurrentsolids leaching system requires from 43% to 85% less fresh water whencompared to conventional leaching techniques base on equivalentthroughput and salt removal.

What is claimed is:
 1. An apparatus for leaching fine solids, theapparatus comprising: a multi-stage countercurrent leaching chamberhaving: a top end; a bottom end; a barren liquor input configured toreceive barren liquor; two or more regions for countercurrent mixing andseparation of liquid and solid phases; and a barren solids outputconfigured to collect and discharge barren solids from the bottom end ofthe multi-stage countercurrent leaching chamber; a fluidized bed chamberwith a top and bottom end, and joined at its top end with the top end ofthe multi-stage countercurrent leaching chamber, the fluidized bedchamber including a pregnant solids input configured to receive afluidizable slurry of pregnant solids; and a clarifier chamber with atop and a bottom end, and joined at its bottom to the top end of themulti-stage countercurrent leaching chamber and the top end of thefluidized bed chamber.
 2. The apparatus of claim 1, wherein thefluidized bed chamber and the multi-stage countercurrent leachingchamber are separated by a shared partition wall furnished with anaperture through which solids can move from the fluidized bed chamberand into the multi-stage countercurrent leaching chamber.
 3. Theapparatus of claim 2, wherein said shared partition wall is furnishedwith an aperture, near the top of said shared partition wall, saidaperture configured to allow transfer of solids at uniform mass fluxover the area of the aperture, and from the fluidized bed chamber intothe top end of the multi-stage countercurrent leaching chamber.
 4. Theapparatus of claim 1, wherein the two or more regions for countercurrentmixing and separation of liquid and solid phases is an arrangement ofinclined fixed thickener plates.
 5. The apparatus of claim 4, whereinsaid inclined fixed thickener plates are arranged at an angle with ahorizontal that is equal to or greater than a submerged angle of reposeof the settled solids generated from the pregnant solids fed to themulti-stage countercurrent leaching chamber.
 6. The apparatus of claim4, wherein said inclined fixed thickener plates are affixed in analternating array on two opposing inside walls of the multi-stagecountercurrent leaching chamber, and spaced such that solids fallingfrom at least a first of the thickener plates will intercept an uppersurface of a thickener plate located below and opposite the at least afirst of the thickener plates.
 7. The apparatus of claim 6, wherein thesolids falling from the at least a first of the thickener platesintercept the upper surface of the thickener plate below the at least afirst of the thickener plates at a point on the thickener plate belowthat is no greater than one-half of a length of the thickener platebelow, wherein the length is measured from an attachment point of thethickener plate below.
 8. The apparatus of claim 4, wherein given avertical axis drawn from a bottom end of one of the thickener platesthrough a point on another thickener plate below and opposing the one ofthe thickener plates, a distance along this vertical axis between apoint where the vertical axis intersects the end of the one of thethickener plates and the point on the another thickener plate is lessthan 20% of a horizontal distance between the end of the one of thethickener plates and an opposing wall of the multi-stage countercurrentleaching chamber.
 9. The apparatus of claim 1, wherein the barren solidsoutput is a dewatering screw press.
 10. The apparatus of claim 9,wherein the dewatering screw press provides barren liquor to the bottomend of the multi-stage countercurrent leaching chamber.
 11. A method forleaching fine solids, the method comprising: receiving barren liquor andpregnant solids near a bottom of a fluidized bed to form a mixture;fluidizing the mixture to form a fluidized mixture that moves toward atop of the fluidized bed; the fluidized mixture entering a region near atop of the fluidized bed that is shared with a top of a multi-stagecountercurrent leaching chamber, the region having a larger crosssection than a cross section of either the fluidized bed or themulti-stage countercurrent leaching chamber alone; receiving a leach orwash solution near a bottom of the multi-stage countercurrent leachingchamber; allowing the pregnant solids to descend within the multi-stagecountercurrent leaching chamber via the force of gravity; separatingsolids and liquids via multiple mixing and separating stages of themulti-stage countercurrent leaching chamber; collecting and dischargingbarren solids from a bottom of the multi-stage countercurrent leachingchamber; and collecting and discharging pregnant liquor from a clarifierarranged atop both the fluidized bed and the multi-stage countercurrentleaching chamber.